The present invention relates to a wheel unit for mounting on a suitcase, particularly relates to an automatically extensible and retractable wheel unit for mounting on a corner of a suitcase.
U.S. Pat. No. 4,097,955 disclosed a wheel unit for mounting on a suitcase. The wheel unit has an extensible and retractable wheel for supporting the suitcase while rolling. However, in the operation of the prior wheel unit, a pin is necessary to be pressed manually inwardly. This is inconvenient and therefore required to be improved.